Various devices for internal fixation of bone segments in the human or animal body are known in the art. One type of system is a pedicle screw system, which may be used as an adjunct to spinal fusion surgery, and which provides a means of gripping a spinal segment. This is particularly used within the fields of orthopedic surgery and neurosurgery, in which spinal implants and rods hold vertebral members in position relative to one another.
The spinal column is a highly complex structure that not only allows a degree of flexible movement in many directions, but also serves to cover and protect veins, arteries, and nerves essential to the body. The adult human spine contains more than twenty discrete bones coupled to one another through posterior facet joints and cartilage. Adjacent muscles coordinate movement in many directions. Various systems have been designed with the intent to provide the vertebrae immobilization when needed for the repair of damaged portions of the spine. Typical spinal fixation devices are implanted in the spine or spinal column and are classified as anterior, posterior, or lateral implants. Of particular interest, rod assemblies may be used as a spinal fixation device and generally include pedicle screws securing rods between various vertebrae.
A conventional pedicle screw system includes a pedicle screw, a rod-receiving device, and a rod. The pedicle screw includes an externally threaded stem and a head portion. The rod-receiving device is coupled to the head portion of the pedicle screw after insertion of the pedicle screw. Subsequently, the rod-receiving device securely receives a rod (commonly referred to as a distraction rod). Two such systems are inserted into respective vertebrae and adjusted to distract and/or stabilize a spinal column, for instance during an operation to correct a herniated disk, by one or more rods. The pedicle screw does not, by itself, fixate the spinal segment, but rather operates as an anchor point to receive the rod-receiving device, which in turn receives the rod. One goal of such a system is to substantially reduce and/or prevent relative motion between the spinal segments that are being fused.
When placing the rod in a plurality of rod-receiving devices, the rod-receiving devices are rarely oriented in a perfectly linear position. More particularly, the varying size of adjacent vertebrae and the often mis-alignment of vertebrae cause the rod receiving devices placed in substantially consistent portions of the vertebrae structure to not be linearly aligned. Consequently, the surgeon often bends or otherwise manipulates the rod during insertion.
Although conventional prior art pedicle screw systems exist, they lack the features that enhance and or benefit newer, minimally invasive surgery (MIS) techniques that are more commonly being used for spinal surgeries. Conventional pedicle screw systems and even more recently designed pedicle screw systems have several drawbacks. Particularly, a number of conventional pedicle screw systems are rather large and bulky, which may result in unnecessary tissue damage in and around the surgical site when the pedicle screw system is installed during surgery. Additionally, a number of conventional pedicle screw systems have a rod-receiving device that is pre-operatively coupled or attached to the pedicle screw, thereby limiting the options available to a surgeon and results in these systems being more difficult to install and maneuver, particularly in conjunction with an MIS technique. In addition, some of the traditional pedicle screw systems include numerous components that must all be carefully assembled together.
Additionally, traditional pedicle screw systems are configured to receive and securely couple substantially straight rods. That is, traditional pedicle screw systems are not well suited for securely coupling a curved rod due to the varying points of contact of the rod with the pedicle screw if the rod is bent a substantial amount.